The invention- relates to cardiac pacemaker leads in general, and more particularly to improvements in multipolar cardiac pacemaker leads.
U.S. Pat. No. 4,590,950 granted May 27, 1986 to Iwaszkiewicz et al. discloses a bipolar cardiac pacemaker lead wherein a distal electrode tip is located a specified distance away from an indifferent ring electrode. Each of the two electrodes is connected to a discrete conductor in the form of helically wound wire, and the ring electrode is dimensioned in such a way that its outer diameter matches the outer diameter of a sleeve-like insulator for the helically wound wires. The ring electrode is not positively connected to any other part but is merely a press fit on the insulator. One or more bridging wires are used to establish an electrical connection between the ring electrode and the corresponding helically wound wire, and each bridging wire extends through the sleeve-like insulator. The absence of positive connections between the bridging wires and the parts which are in electric contact therewith renders it possible to extract the helically wound wire or wires and thus render the lead useless for its intended purpose.
German Pat. No. 30 43 189 C3 granted Jul. 12, 1984 to Osypka discloses a cardiac pacemaker lead wherein the proximal pacing electrode is a sleeve. The terminal or terminals of the corresponding helically wound wire are caused to pass through an insulating sleeve and are affixed to the sleeve-like electrode.
German patent application No. 37 18 324 A1 of Hirschberg (published Dec. 22, 1988) discloses a cardiac pacemaker lead which employs conductors having different diameters. The sleeve-like pacing electrode is slipped over the end portion of the larger-diameter conductor and directly engages such end portion because the corresponding portion of the sleeve-like insulator is removed together with insulation on the end portion of the larger-diameter conductor. This proposal exhibits the drawback that the utilization of conductor wires having different wire diameters as well as convolutions of different diameters contributes to the initial and assembly cost of the lead. The stability of the lead is unsatisfactory, partly due to movements of the heart in which the electrodes of the lead are implanted and partly due to the absence of positive electrical connections between the wires and the respective electrodes. Still further, the danger of short-circuiting the lead is ever present because the movements of the heart are likely to entail the establishment of electric contact between the smaller-diameter convolutions and the sleeve-like proximal electrode.
European patent application No. 0 292 596 A1 of Hirschberg (published Nov. 30, 1988) discloses a method of electrically connecting conductors and electrodes in an implantable electrode lead. The inventor proposes to employ a curved tool which serves to extract a portion of a conductor which is embedded in two insulating layers. The thus extracted portion of the conductor can be connected to a composite pacing electrode, namely an electrode having two coaxial sleeves which are turned relative to each other so that the extracted portion of the conductor is clamped between the internal surface of the outer sleeve and the external surface of the inner sleeve. Such proposal exhibits the drawback that the two sleeves of the electrode are likely to shear off the exposed portion of the conductor. Movements of the electrode upon implantation into the heart of a patient are likely to interrupt the electrical connection between the sheared off portion and the major portion of the electrode. Moreover, it is rather difficult or plain impossible to inspect the quality and reliability of the connection between the conductor and the electrode, especially in the regions where the exposed portion of the conductor is engaged by the edges of the inner sleeve of the electrode.
German patent application No. 36 40 033 A1 of Hirschberg (published May 26, 1988) discloses a cardiac pacemaker lead wherein the helically wound wires of the conductors are reinforced in that the neighboring convolutions of certain portions of such conductors are fixedly connected to each other. This results in undesirable stiffening of the lead which can create problems during implantation.
U.S Pat. No. 4,387,727 granted Jun. 14, 1983 to Sandstrom discloses a coaxial service kit which is used to splice body implantable bipolar leads of the type having coaxial inner and outer coil wire conductors. The patentee proposes to employ a conductive pin and a set screw.
U.S. Pat. No. 4,628,943 granted Dec. 16, 1986 to Miller discloses a bipolar screw-in pacing lead assembly wherein the proximal electrode is electrically connected to the respective helically wound wire-like conductor by a brush contact.
French patent application No. 81 19037 of Sandstrom et al. (published Apr. 15-16, 1982) discloses a cardiac pacemaker lead wherein a helically wound-wire-like conductor is surrounded by an insulating sheath and is in contact with several axially parallel internal conductors. A sleeve-like electrode is slipped onto the sheath so that it frictionally engages the internal conductors and the sheath.